perf tools: Compare hists comm by addresses

Now that comm strings are allocated only once and refcounted to be shared
among threads, these can now be safely compared by addresses. This
should remove most hists collapses on post processing.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1381468543-25334-8-git-send-email-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/sort.c

@@ -80,7 +80,8 @@ struct sort_entry sort_thread = {
 static int64_t
 sort__comm_cmp(struct hist_entry *left, struct hist_entry *right)
 {
-	return right->thread->tid - left->thread->tid;
+	/* Compare the addr that should be unique among comm */
+	return thread__comm_str(right->thread) - thread__comm_str(left->thread);
 }
 
 static int64_t